This project concerns the morphologic and immunologic aspects of an investigation into the presence of MHV virus in spontaneous hepatomas in CBA/H-T6T6 mice. These mice carry a latent hepatotrophic virus which can be unmasked by neonatal thymectomy, or by administration of cortisone. There is some preliminary evidence that this is mouse hepatitis virus. A high proportion of the same animals, left in natural condition to old age, develop spontaneous hepatomas, most of which contain large numbers of cytophasmic inclusion bodies. Our objective is to examine the possibility that the latent virus is causally related to the hepatomas. We propose to study the hepatomas by electron microscopy with particular attention to the inclusions, for morphologic evidence of virus. Any presumed viral particles will be compared with those seen in Swiss mice which have developed hepatitis after injection of MHV virus. Viral antigens in hepatomas will be sought by immunofluorescent techniques using hyperimmune sera induced in rabbits by MHV virus. The inclusions will be studied by histochemical techniques to indicate whether they are viral in nature. Hepatitis will be induced in T6T6 animals by neonatal thymectomy and by cortisone, and will be similarly studied by light and electron microscopy and by use of hyperimmune sera directed against MHV virus.